Suddenly, as we round a bend, the trees are gone. Barren stretches of rock and cobblestone line the shore. Jungle is visible only in the distance.

“We are coming to the mining,” says Ortiz.

Ahead of us, nosed against the stony banks, countless dredge barges are anchored. Each is fitted with a roof for shade, a large motor on deck and a huge suction pipe running from the stern into the water. Silt and stones extracted from the river bottom are sprayed into a sluice positioned on the bow and angled onto shore. The sluice is lined with heavy synthetic matting, similar to indoor-outdoor carpet. As silt (the source of gold) is trapped in the matting, stones hurtle down the incline, crashing in great mounds on the banks. Thousands of rocky hillocks litter the shoreline.

As we pass one barge—its blue-painted steel hull faded by the intense sun—the crew members wave. We beach our barca and clamber over the stone-strewn shore toward the barge, moored along the bank. A man who appears to be in his 30s tells us that he has mined along the river for several years. He and his family own the barge. The entire clan, originally from Puerto Maldonado, lives aboard much of the time, bunking in handmade beds on deck beneath mosquito nets and eating from a galley kitchen run by his mother. The din from the dredging engine is deafening, as is the thunder of rocks tumbling into the sluice.

“About $70 most days, but sometimes as much as $600. Much, much more than many people back in the town make in a whole month. It’s hard work, though.” Princely though this renumeration may seem to the miner, it is only a fraction of the price an ounce of gold will command once it passes through the hands of countless middlemen.

Roughly 80 miles southwest of Puerto Maldonado, the gold rush boomtown of Huepetuhe lies at the foot of the Andes. It’s the summer of 2010. Muddy streets are pocked with puddles the size of small ponds. Pigs root everywhere. Boardwalks keep pedestrians—at least those not too muddy or inebriated to care—out of the slop. Makeshift wooden-plank structures, many on stilts, are roofed in patched corrugated metal. From their stalls, vendors sell everything from automobile piston rings to potato chips. There are rough little bars and open-air restaurants. Along the main street are dozens of shops where gold is assayed, weighed and bought.

Behind town, in the Huepetuhe River valley, virgin rainforest has been razed. “When I first came here, 46 years ago, I was 10 years old,” Nico Huaquisto, a resident, recalls. “The Huepetuhe River was maybe 12 feet wide and its water ran clear. Along the river’s edges, there was jungle all around. Now—just look.”